CD40 is a cell surface phosphorylated glycoprotein that is expressed on a variety of cell types, including B cells, B cell malignancies, follicular dendritic cells, basal epithelial cells, and carcinomas. CD40 binds CD40 ligand (“CD40L”). CD40L is expressed on activated T cells during inflammation and cancer (Younes et al., 1998, Br. J. Haematol. 100:135-141; for areview see Grewal and Flavell, 1998, Annu. Rev. Immunol. 16:111-135). The interaction of CD40 with CD40L results in B cell activation and proliferation of normal B cells; however CD40-mediated signaling in B cell-derived tumor lines can result in activation-induced cell death. The strength of the activation signal is key to activation-induced tumor cell death (Grafton et al., 1997, Cell. Immunol. 182:45-56). Therefore, compositions and methods for increasing receptor-ligand interaction and strength of activation signal between CD40 and CD40L would be of great value in treating disease.
2.1 CD40 and CD40 Ligand
CD40 is a member of the TNF receptor superfamily. This family includes TNFrII, CD40, CD30, LMP-1, LTBr, ATAR, OX-40 and 4-1BB receptors. CD40 is constitutively expressed on B-lymphocytes, macrophages and dendritic cells and is induced by cytokine activation on fibroblasts, endothelial cells and epithelial cells (Van Kooten and Banchereau, 1997, Curr. Opin. Immunol., 9: 330-337). CD40 has also been shown to be highly expressed on many human carcinomas including lung, bladder, gastric, breast and ovarian cancers (Stamenkovic et al., 1989, EMBO J. 8:1403-1410).
The ligand for CD40 is a membrane protein that is expressed on activated T cells. Receptor binding of CD40L results in CD40 multimerization, the generation of activation signals (for antigen presenting cells such as dendritic cells, monocytes and B cells) and the generation of growth and differentiation signals (for cytokine-activated fibroblasts and epithelial cells). CD40 signals are transduced from the multimerized receptor via recruitment of a series of TNF receptor-associated factors (“TRAFs”) (Kehry, 1996, J. Immunol. 156:2345-2348). Subsets of TRAFs interact differentially with TNF family members, including CD40, to provide stimuli to a wide variety of downstream pathways. TRAF1 and TRAF2 are implicated in the modulation of apoptosis (Speiser et al., 1997, J. Exp. Med. 185:1777-1783; Yeh et al., 1997, Immunity 7:715-725). TRAFs 2, 5, and 6 participate in proliferation and activation events, including NF-kB and c-Jun N-terminal kinase activation. In normal B cells, binding of CD40 recruits TRAF2 and TRAF3 to the receptor complex and induces down-regulation of other TRAFs (Kuhune et al., 1997, J. Exp. Med. 186: 337-342). The effects of CD40 binding are also dependent on membrane density (De Paoli et al., 1997, Cytometry 30:33-38). Importantly, unlike the proliferative response seen with normal primary B cells, CD40 binding on neoplastic B cells can result in growth inhibition and activation-induced cell death (Funakoshi et al., 1994, Blood 83:2787-2794). Thus, CD40 activation in the context of different cell types, transformation, resident TRAFs and co-stimuli can induce responses ranging from activation and proliferation to growth inhibition and apoptosis.
2.2 Anti-CD40 Antibodies
With at least one exception, the anti-CD40 monoclonal antibodies (“mAbs”) described to date are of three general classes: (1) those that block CD40/CD40L interaction by at least 90% and have anti-neoplastic properties (Armitage et al., U.S. Pat. No. 5,674,492; Fanslow et al., 1995, Leukocyte Typing V, Schlossman et al., eds., 1:555-556); (2) those that antagonize signaling through CD40 (deBoer et al., U.S. Pat. No. 5,677,165); and (3) those that deliver a stimulatory signal through CD40 but do not increase the interaction between CD40 and CD40L, e.g., G28-5, (Ledbetter et al., U.S. Pat. No. 5,182,368; PCT Publication WO 96/18413).
One mAb, CD40.4 (5C3) (PharMingen, San Diego, Calif.), has been shown to increase the interaction between CD40 and CD40L by approximately 30-40% (Schlossman et al., eds., 1995, Leukocyte Typing V: White Cell Differentiation Antigens 1:547-556).
Armitage et al. (U.S. Pat. No. 5,674,492) describes methods using CD40 binding proteins, including mAb HuCD40-M2, that are capable of binding CD40 and inhibiting the binding of CD40 to CD40L, for preventing or treating disease characterized by neoplastic cells expressing CD40.
DeBoer et al. (U.S. Pat. No. 5,677,165) describes anti-CD40 mAbs that, being free of significant agonistic activity, bind to CD40 on the surface of B-cells, and block B-cell activation. An essential feature of U.S. Pat. No. 5,677,165 is that upon binding of the anti-CD40 mAb to human CD40 on the surface of normal human B cells, the growth or differentiation of normal human B cells is inhibited.
Ledbetter et al. (U.S. Pat. No. 5,182,368) describes a ligand, G28-5, that binds to the B cell surface antigen Bp50 (now designated CD40) and stimulates activated B cells to traverse the cell cycle such that B cell proliferation is augmented. However, G28-5 does not enhance activation of B cells in the presence of CD40L, and does not potentiate CD40/CD40L interaction.
S2C6 is an anti-CD40 mAb that was prepared against a human bladder carcinoma (Paulie et al., 1984, Cancer Immunol. Immunother. 17:165-179). S2C6 binds to the CD40 receptor expressed on a variety of cell types including B-lymphocytes, endothelial and epithelial cells. S2C6 has been shown to have specificity toward neoplastic urothelium and B cell-derived malignant lymphocytes. Reactivity with a prostatic carcinoma cell line, HS, and weak reactivity with a melanoma has also been shown (Paulie et al., 1984, Cancer Immunol. Immunother. 17:165-179). Studies have suggested the utility of S2C6 as a diagnostic marker for B cell malignancies (Paulie et al., 1984, Cancer Immunol. Immunother. 17:165-179; Paulie et al., 1985, Eur. J. Cancer. Clin. Oncol. 21:701-710). In addition to detecting B cell malignancies, S2C6 has been shown to deliver strong growth-promoting signals to B lymphocytes (Paulie et al., 1989, J. Immunol. 142:590-595).
S2C6 has agonistic activity on human peripheral B cells as demonstrated by its ability to stimulate primary B cell proliferation in a dose dependent manner (Paulie et al., 1989, J. Immunol. 142:590-595).
Although competition studies have shown that G28-5 and S2C6 bind the same or proximal epitopes, the antibodies have been determined to be functionally different based primarily on the stated magnitude of stimulation achieved by either mAb on previously stimulated tonsillar B cells (Clark and Ledbetter, 1986, Proc. Natl. Acad. Sci. USA 83:4494-4498; Ledbetter et al., U.S. Pat. No. 5,182,368). One hundred times more S2C6 compared to G28-5 was required to achieve tonsillar B cell activation under the specific conditions tested (Ledbetter et al., U.S. Pat. No. 5,182,368).
There is a need in the art for therapeutics with increased efficacy to treat or prevent cancer, activate or augment the immune system or treat or prevent an immune deficiency or disorder, a need provided by the present invention.
Citation or identification of any reference herein shall not be construed as an admission that such reference is available as prior art to the present invention.